This invention relates to an analytical microsyringe usable as in gas chromatography and liquid chromatography.
As illustrated in FIG. 7, the microsyringe of this kind generally comprises a syringe body 1 made of glass, an injection needle 2 fixed to the leading end part of the syringe body 1, a linear metallic plunger 3 slidable inside the syringe body 1 and a knob 4 mounted on the rear end of the plunger 3. It is used in injecting a stated amount of a gaseous or liquid sample into an analytical apparatus.
For the purpose of enabling a minute amount of the sample to be introduced into and discharged out of the syringe body 1, the microsyringe is configured so as to produce close sliding engagement between the inner surface of the syringe body 1 and the outer surface of the plunger 3.
Since the prior art microsyringe uses the plunger 3 formed of stainless steel wire or piano wire of small elastic strain, it has a disadvantage that the plunger 3 bends and sustains permanent deformation during the course of use even when the microsyringe is handled fully attentively.
In the case of a microsyringe having a volume of 5-.mu.l and having a plunger 3 which has a diameter of 0.370 mm and a stroke of 46.5 mm, for example, since the diameter of the plunger 3 is very small, it sustains a bend quite naturally in the course of use. When the plunger 3 is bent even slightly, the state of close sliding engagement no longer exists between the outer surface of the plunger 3 and the inner surface of a syringe body 1. The permanent deformation of the plunger 3 mentioned above prohibits a gaseous or liquid sample from being introduced into and discharged out of the syringe body 1 precisely in a minute amount and spoils the function of the microsyringe. For this reason, the microsyringes of the latest development are provided with various means for protecting the plunger 3 against such a bend, as illustrated in FIGS. 8A to 8D.
A prior art microsyringe illustrated in FIG. 8A is provided with a tubular protector 5A made of Teflon (polytetrafluroethylene) in stated dimensions and disposed on the side of the plunger insertion mouth of a syringe body 1, so that the guiding action of the tubular protector 5A may enable the plunger 3 to slide closely on the syringe body 1. A tubular protector 5B of another prior art microsyringe illustrated in FIG. 8B is of a telescopic structure.
In still another prior art microsyringe illustrated in FIG. 8C, a guide bar 6 is attached to a knob 4 in such a manner as to extend in parallel to a plunger 3 and this guide bar 6 is slidably supported in place by a holder 7 disposed on a syringe body 1, so that the slide of the guide bar 6 against the holder 7 may enable the plunger 3 to slide on the syringe body 1.
FIG. 8D illustrates yet another prior art microsyringe which has a reinforcing pipe 8 set around a plunger 3 so that the reinforcing action of the reinforcing pipe 8 may enable the plunger 3 to slide on a syringe body 1.
Although the conventional means for preventing the plunger from bending are more or less different in structure from one another, they are invariably incapable of completely preventing the plunger 3 of stainless steel wire from sustaining permanent deformation due to bending. In addition, the provision of such bend-preventing means only goes to add to the cost of the microsyringe itself but fails to fully accomplish the object thereof.
In the conventional microsyringes, since the inner surface of the syringe body 1 and the outer surface of the plunger 3 are ground against each other throughout their entire surfaces, the rubbing forcibly scrapes the outer surface of the plunger 3 or the inner surface of the syringe body 1 and gives rise to ground powder between the closely opposed surfaces of the two members, with the result that smoothness of the slide of the plunger 3 will frequently be impaired.